1. Field of the Invention
The invention generally relates to an apparatus, and more particularly to a stability unit and/or enhancer for increasing the stability of liquid jets formed from nozzle plates in the apparatus. Another aspect of the invention relates to operating the apparatus at a condition that reduces the stability of liquid jets, e.g., a droplet generator apparatus. Yet another aspect of the invention relates to operation of the apparatus with an aqueous slurry.
2. Discussion of the Related Art
The absorption of a gas into a liquid is a key process step in a variety of gas liquid contacting systems. Gas liquid contactors, also known as gas liquid reactors, can be classified into surface and volume reactors where the interfacial surface area between the two phases is created at the liquid surface and within the bulk liquid, respectively. There are many examples of surface gas liquid reactors such as rotating disks and liquid jet contactors. Rotating disk generators are disks (rotors) partially immersed in a liquid and exposed to a stream of gas. A thin film of liquid solution is formed on the rotor surface and is in contact with a co-current reagent gas stream. The disk is rotated to refresh the liquid reagent contact with the gas. In a volume gas liquid reactor, the gas phase is dispersed as small bubbles into the bulk liquid. The gas bubbles can be spherical or irregular in shape and are introduced into the liquid by gas spargers. The bubbles can be mechanically agitated to increase the mass transfer.
In many gas liquid contacting systems, the rate of gas transport to the liquid phase is controlled by the liquid phase mass transfer coefficient, k, the interfacial surface area, A, and the concentration gradient, delta C, between the bulk fluid and the gas liquid interface. A practical form for the rate of gas absorption into the liquid is then:Φ=φα=kGa(p−pi)=kLa(CL*−CL)where the variable Φ is the rate of gas absorption per unit volume of reactor (mole/(cm3 s)); φ is the average rate of absorption per unit interfacial area (mole/(cm2 s)); a is the gas liquid interfacial area per unit volume (cm2/cm3, or cm−1); p and pi are the partial pressures (bar) of reagent gas in the bulk gas and at the interface, respectively; CL* is the liquid side concentration (mole/cm3) that would be in equilibrium with the existing gas phase partial pressure, pi; CL (mole/cm3) is the average concentration of dissolved gas in the bulk liquid; and kG (mole/(cm2*s*bar)) and kL (cm/s) are gas side and liquid side mass transfer coefficients, respectively.
In the related art, there are many approaches to maximizing the mass transfer and specific surface area in gas contactor systems. The principal approaches include gas-sparger, wetted wall jet, and spray or atomization. The choice of gas liquid contactor is dependent on reaction conditions including gas/liquid flow, mass transfer, and the nature of the chemical reaction. Table 1 summarizes various mass transfer performance features of some related art gas liquid reactors. To optimize the gas absorption rate, the parameters kL, a, and (CL*−CL) must be maximized. In many gas liquid reaction systems the solubility of the CL* is very low and control of the concentration gradient, therefore, is limited. Thus, the primary parameters to consider in designing an efficient gas liquid flow reactor are mass transfer and the interfacial surface area to reactor volume ratio, which is also known as the specific surface area.
TABLE 1COMPARISON OF CONVENTIONAL GASLIQUID REACTOR PERFORMANCEβ(%, gas liquidkGvolumetric(mole/cm2skLakLaReactor Typeflow rate ratio)atm) ×104(cm/s) ×102(cm−1)(s−1) ×102Packed Column 2-250.03-2 0.4-2 0.1-3.50.04-7.0(counter-current)Bubble Reactors60-980.5-21-40.5-6  0.5-24Spray Columns 2-200.5-20.7-1.50.1-1 0.07-1.5Plate Column10-950.5-6 1-201-2 1-40(Sieve Plate)
There are various gas liquid contacting reactors whose performance is dependent on interfacial contact area. For example, the chemical oxygen iodine laser (COIL) produces laser energy from a chemical fuel consisting of chlorine gas (Cl2) and basic hydrogen peroxide (BHP). The product of this reaction is singlet delta oxygen, which powers the COIL. The present technology uses circular jets of liquid BHP mixed with Cl2 gas to produce the singlet delta oxygen. In a typical generator, the jets are on the order of 350 microns in diameter or smaller. To generate the jets, the liquid BHP is pushed under pressure through a nozzle plate containing a high density of holes. This produces a high interfacial surface area for contacting the Cl2 gas. The higher the surface area, the smaller the generator will be and the higher the yield of excited oxygen that can be delivered to the laser cavity. Smaller and more densely packed jets improve the specific surface area, but are prone to clogging and breakup. Clogging is a serious problem since the reaction between chlorine and basic hydrogen peroxide produces chlorine salts of the alkali metal hydroxide used to make the basic hydrogen peroxide. Clogging also limits the molarity range of the basic hydrogen peroxide, which reduces singlet oxygen yield and laser power. The heaviest element of the COIL system is this chemical fuel. Problems inherent in producing the fuel increase the weight and decrease the efficiency of the COIL laser as a whole. Thus, there exists a need for a COIL laser that has increased efficiency and lower weight than present designs.
In another example, gas liquid contactors are also used in aerobic fermentation processes. Oxygen is one of the most important reagents in aerobic fermentation. Its solubility in aqueous solutions is low but its demand is high to sustain culture growth. Commercial fermenters (>10,000 L) use agitated bubble dispersion to enhance the volumetric mass transfer coefficient kLa. The agitation helps move dissolved oxygen through the bulk fluid, breaks up bubble coalescence, and reduces the boundary layer surrounding the bubbles. The interfacial area in these systems is increased by increasing the number of bubbles in the reactor and reducing the size of the bubble diameter. However, oxygen mass transfer to the microorganism is still constrained by the relatively small interfacial surface area of the bubble and the short bubble residence times. Current sparger systems (bubble dispersion) show a relatively small volumetric mass transfer coefficient kLa, (about 0.2/s); therefore, a new approach for generating maximum interfacial surface area is desired to overcome these mass transfer limitations.
In designing systems for industrial applications, consideration must be given to both cost and efficiency. Conventional wisdom generally precludes that both can be optimally obtained simultaneously. In the case of gas liquid contactors, the conventional wisdom is generally maintained in industrial applications such as chemical processing, industrial biological applications, pollution control, or similar processes requiring reacting or dissolving a gas phase chemistry with a liquid phase in a dynamic flow system.
In the example of pollution control, the standard methodology of removing a target compound or compounds in a wet process is a countercurrent flow system utilizing fine droplets of liquid phase falling through a flowing gas phase 180° in an opposite direction. Normally, gravity is used to draw the liquid phase to a capture sump at the base of a column or tower. The gas phase flows up through the same column or tower. This gas phase is then captured for further processing or released to the atmosphere.
In order to accommodate for larger scale chemical processes, the column or tower must be scaled linearly with the size of the desired process either by length or diameter. The current logical methodology is to increase the scale of a single unit process since capital costs of a single unit process generally do not scale linearly with size.
Another downside of standard countercurrent, gravitational or aerosol/droplet gas liquid contactors is that gas flows must be at a low enough velocity such that gravity effects are greater than the buoyancy of the droplets. Regardless, significant evaporation of the liquid reactant generally does occur since contact times are long, requiring significant capture of that vapor prior to secondary processing or release.